Stimulatory effects of CpG ollgodeoxynucleotide on dendritic cell-based immunotherapy of colon cancer in CEA/HLA-A2 transgenic mice

Immunostimulatory DNA containing unmethylated cytosine-guanine (CpG) motifs have been successfully used as adjuvants to enhance the immunity of vaccines designed to trigger antitumor T-cell responses. We examined the effect of a CpG oligodeoxynucleotide (CpG ODN) for its ability to potentiate the activity of tumor antigen-pulsed dendritic cells (DC) in a clinically relevant mouse model, which is transgenic for both careinoembryonic antigen (CEA) and HLA-A2 for the treatment of colon carcinoma in a therapeutic setting. The systemic administration of CpG ODN 1826 alone had modest effect on tumor growth when tumors were palpable and had no effect with larger tumor burden. However, coadministration of CpG ODN 1826 with the vaccine provided significant increase in tumor-free survival compared with mice immunized with DC-based vaccines alone. The DC/CpG combined vaccination strategy resulted in increased secretion of Thl cytokines and HLA-A2-restrieted CEA-speciflc CTL responses were also enhanced. Both tumor regression and extended tumor-free survival resulting from DC/CpG combination therapy required the participation of T cells. Tumor-free mice were resistant to tumor rechallenge and immunity conferred by the vaccine was transferable in athymic nude mice. These results provide evidence that vaccination with antigen-pulsed DC with CpG ODN as adjuvant can lead to effective tumor regression and long-term survival in a murine model of colon carcinoma.